cochlear deafness

7/30/2019 Cochlear Deafness

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Cochlear Deafness


2/15

Causes

congenital aplasia

labyrinthitis (viral, bacterial)

ototoxic drug: streptomycin, kanamycin,garamycin, neomycin, quinine, alcohol

sudden deafness

head trauma/trauma kapitis noise-induced


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Clinical Manifestation

recruitment: unable to hear soft sound, but

loud sound is uncomfortable

able to hear sound, but difficult to understand

conversation


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Investigation: special audiometry

SISI (Short Increment Sensitivity Index) test

ABLB (Alternate Binaural Loudness Balance)test

Speech audiometry

Bekessy Audiometry

Objective audiometry:

Impedance audiometry

Otoacoustic emission

BAER


5/15

SISI test

detect recruitment phenomenon determine the pts hearing treshold

give stimuli 20 dB above hearing treshold

give additional 5 dB stimuli

reduce stimuli to 4, 3, 2, 1 dB pts able to discriminate + SISI

or:

increase stimuli 1 dB every 5s up to 20 times

count how many times pts able to discriminate the differences

+ if 70 100% score 0 70% : not specific, maybe normal or other perceptive

deafness


6/15

ABLB test

requires:

- normal hrg in one ear at freq to be used

- difference in

between ears > 25 dB tones pulse alternating between ears 2 or 3 times

per judgement.

pt is asked which ear is louder or same

begin at 20 SL in poorer ear, 0 SL in better ear.

adjust level in better ear 5 dB steps


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find level where loudness judged equal.

increase poorer ear by 10 or 20 dB and repeat

adjustments in better ear.

plotting result:

Use the LADDERGRAM

Connect decibel values judged equally loud


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Speech audiometry

obj: to assess pts ability in daily conversation, or to assess the needof hearing aid

pts asked to repeat heard word from recorder

cochlear deafness: pts unable to discriminate S R C N H CH

interpretation of speech discrimination score:

90 100%: normal 75 90%: mild hearing loss

60 75%: moderate hearing loss

50 60%: difficult to follow daily conversation


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Bekessy audiometry

given interrupted and continuous sound

pts responds by pressing button when a soundheard

N: amplitude 10 dB recruitment: amplitude


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I: C and I overlap: norm or cond.

II: C below I at freqs of HL: Cochlear

III: I follows loss, C drops to bottom: RetroIV: C below I by 20-25 dB: Coch or Ret

V: I below C: False hearing loss


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Loudness Growth Patterns

0

20

40

60

80

100

120

10 30 50 70

Normal

Cochlear

Retro-cochlear


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Impedance Audiometry

decrease treshold of acoustic reflex


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Otoacoustic Emission

=cochlear response produced by outer hair

cell

with probe, microphone, loudspeaker


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Brainstem Auditory Evoked-Response

wave:

I: cochlea

II: cochlear nucleus

III: superior olivary nucleus

IV: lateral lemniscus

V: inferior colliculi

cochlear deafness

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